This invention relates in general to vehicle drum brake assemblies and in particular to an improved damped anchor shim for use in such a vehicle drum brake assembly.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies can be actuated by hydraulic, pneumatic, or mechanical pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like. The structure and operation of both drum brake assemblies and disc brake assemblies, as well as the actuators therefor, are well known in the art.
A typical drum brake assembly includes a backing plate which is secured to a fixed, non-rotatable component of the vehicle, such as the vehicle axle housing, and an abutment assembly secured to the backing plate. A pair of opposed arcuate brake shoes are supported on the backing plate for selective movement relative thereto. Each of the brake shoes has a friction pad or lining secured thereto. Each of the brake shoes includes a lower end which engages a portion of the abutment assembly so as to pivotally support the brake shoes relative to the backing plate. In order to maintain the lower ends of the brake shoes in engagement with the abutment assembly, a spring is typically secured to the shoes adjacent the lower ends thereof and urges the shoes into engagement with the abutment assembly.
The drum brake assembly further includes a hollow cylindrical brake drum which is secured to the vehicle wheel for rotation therewith. The hollow interior of the brake drum defines an inner cylindrical braking surface. The brake drum is disposed adjacent to the backing plate such that the brake shoes extend within the cylindrical braking surface. To effect braking action, the brake shoes are moved outwardly apart from one another such that the friction pads frictionally engage the cylindrical braking surface of the brake drum. Such frictional engagement causes slowing or stopping of the rotational movement of the brake drum and, therefore, the wheel of the vehicle in a controlled manner.
One or more actuating mechanisms are provided in the drum brake assembly for selectively moving the brake shoes outwardly apart from one another into frictional engagement with the cylindrical braking surface of the brake drum. Usually, a hydraulically or pneumatically actuated service brake mechanism is provided for selectively actuating the drum brake assembly under normal operating conditions. Such a service brake mechanism can include a hydraulic cylinder having a pair of opposed pistons which abut and move the brake shoes apart from one another into frictional engagement with the cylindrical braking surface of the brake drum. A mechanically actuated parking and emergency brake mechanism is also usually provided for selectively actuating the drum brake assembly. The parking and service brake mechanism can include an actuating lever pivotally supported on one of the brake shoes. The actuating lever is connected to a cable which, when pulled, moves the brake shoes apart from one another into frictional engagement with the cylindrical braking surface of the brake drum.
As discussed above, the lower ends of the brake shoes are in engagement with the abutment assembly. Also, since the abutment assembly is operative to transfer braking torque during braking from the associated brake shoes to the frame of the vehicle, undesirable vibration, rattle or other noises may be transmitted to the frame during such braking. To prevent this from occurring, it is known to provide an anti-rattle clip in the drum brake assembly. The anti-rattle clip is typically embodied as a flat spring metal member attached to the abutment assembly. The anti-rattle clip is operative to exert a force against the associated brake shoes to prevent them from rattling while limiting pad sliding resistance to an optimum level when the drum brake assembly is disengaged. A number of anti-rattle clip structures are known in the art for use with the friction pads of drum brake assemblies.
This invention relates to an improved drum brake assembly having at least one damped brake shoe anchor shim support device secured to an associated backing plate which is effective to reduce brake noise during actuation of the drum brake assembly. The drum brake assembly includes a backing plate, a pair of brake shoes supported on the backing plate for selective movement into frictional engagement with a brake drum, a brake mechanism, and an abutment assembly secured to the backing plate. Each of the brake shoes includes a first end and an opposite second end. The drum brake assembly further includes a brake mechanism adapted to engage the first ends of the brake shoes so as to cause the brake shoes to move outwardly into frictional engagement with the brake drum. The abutment assembly includes an inner retainer plate disposed adjacent the backing plate, an outer retainer plate, and an anchor shim carried by the inner retainer plate and interposed between the backing plate and the retainer outer plate. The anchor shim includes an inner surface and an outer surface which is adapted to contact the second ends of the brake shoes. The anchor shim includes a damping material applied to the inner surface thereof so as to be disposed between adjacent contacting areas of the outer surface of the inner retainer plate and the inner surface of the anchor shim to thereby reduce the transmission of noise from the brake shoes through the abutment assembly to the backing plate.
Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.